Roberto Simonini

Effects of temperature on two Mediterranean populations of Dinophilus gyrociliatus (Polychaeta: Dinophilidae): I. Effects on life history and sex ratio

Abstract The effects of temperature on the life history characteristics of two populations of the polychaete Dinophilus gyrociliatus , one from Ravenna (northern Adriatic Sea) and the other from Genoa (Ligurian Sea), were investigated. The temperatures tested (6, 12, 18, 24 and 30 °C) cover a wider range than those prevailing in the natural environment. In the populations studied there are broad differences in timing of development and reproduction. At 6 °C, the adults of both populations survive for a long time but they are unable to reproduce. At 12 °C, only the animals from Ravenna manage to reproduce. At the higher temperatures (18, 24 and 30 °C), the development of the animals belonging to the Genoa strain is faster than that of the Ravenna strain. The duration of the various phases of the biological cycle is very similar in both populations, but that from Ravenna exhibits greater tolerance of low temperatures, slower development rate and lower development threshold temperature than does the Genoa population. Temperature and geographical origin also have strong effects on reproductive characteristics. The highest fecundity values were observed at 12 °C in the Ravenna strain, the lowest at 30 °C in both groups. At 18 °C, the Genoa population is more fecund than the Ravenna one, while the situation is reversed at 12 °C. The smallest ovigerous capsules are produced at 30 °C, the biggest at 12 °C, and the Genoa females produce larger capsules than do the females from Ravenna, except at 12 °C. The size of both male and female eggs varies in relation to temperature, the smallest female eggs generally being laid at the higher temperatures. At all the temperatures tested, the sex ratio of the Ravenna population is higher than that of the Genoa population. In the Ravenna strain, temperature has no effect on the sex ratio, while in the Genoa strain the sex ratio at 24 °C is lower than at 18 and 30 °C. Comparison of the two populations at the same temperature reveals considerable differences in the characteristics of their respective life histories and sex ratios. It is very likely that the extreme selectivity of the harbor environments has favored the fragmentation of the species into differentiated populations that have adapted to the conditions prevailing in the different localities.

Novel antifouling agent--zinc pyrithione: short- and long-term effects on survival and reproduction of the marine polychaete Dinophilus gyrociliatus.

The recent ban on TBT in boat antifouling paints has resulted in a large employment of the biocide zinc pyrithione (ZnPT) as substitute. Despite concerns of its environmental toxicity at ultra-trace concentrations, ZnPT has received little attention, as it was assumed to photo-degrade easily. However, recent evidence has suggested that ZnPT degrades only partially, and persists in the marine environment, especially where the influence of light is limited, such as in harbours. Short-term acute toxicity tests and life table response experiments (LTREs) were performed to evaluate the effects of ZnPT on the polychaete Dinophilus gyrociliatus at both individual and population level. The 96h-LC(50) values for ZnPT on D. gyrociliatus were 7.8 and 11.5nM under dark and 12h light/12h dark conditions, respectively. In LTREs, laboratory cultured cohorts of D. gyrociliatus were exposed to sublethal concentrations of ZnPT (0.5 and 1nM) and compared to a control cohort. The survival among individuals exposed to the highest concentration decreased already during the 2nd week of life with respect to the control. The effects of the biocide on fecundity were even more evident: ZnPT caused a considerable reduction in both the exposed groups. The demographic approach applied here succeeded in identifying ZnPT effects both on the biological cycle and on the growth potential of polychaete D. gyrociliatus. The net growth rate (R(0)) appeared to be the demographic parameter most sensitive to ZnPT, as the biocide exposure was associated with a sharp decline of R(0) in both the 0.5 and the 1nM groups (-41% and -63%, respectively) in comparison to the control cohort. The population growth rate lambda (often used as an index of population fitness) and the life expectancy e(0) were also significantly reduced, while ZnPT exposure did not affect the generation time T. These results highlight the potential ecological threat posed by the biocide ZnPT, even at the very low tested concentrations, which are already detectable in some European marinas.

Effects of zinc exposure on the polychaete Dinophilus gyrociliatus: a life-table response experiment

A life-table response experiment (LTRE) was performed in order to study the effects of enhanced zinc on the survival, fecundity and demographic indices of Dinophilus gyrociliatus (Polychaeta). A control group and three treated cohorts kept in artificial seawater enriched with nominal concentrations of zinc at 0.25, 0.50 and 1.00 microg Zn/ml, respectively, were considered. Zinc marginally affected survival but had a strong impact on the reproduction of D. gyrociliatus. Zinc enrichment had no effect on age at maturity, whereas it induced a slight increase in fecundity during the early reproductive phases at 0.50 and 1.00 microg Zn/ml, and a sharp decrease in fecundity from the 20th day of life at all levels of metal enrichment tested. Treated groups were characterised by a marked reduction of the net growth rate (R0) and a decrease in generation time (T) with respect to the control groups, but no effect on life expectancy (e0) or on population growth rates (lambda) was observed. R0 and lambda, which are the most commonly used indices of fitness, were not equally susceptible to zinc. Lambda appears less sensitive to stress induced by metal enrichment with respect to R0 and other life history traits like age-specific fecundity. D. gyrociliatus appears to be an appropriate bioindicator species in LTRE to assess the consequences of environmental heavy metals on individual life-history and population dynamics.

Responses of a Northern Adriatic Ampelisca–Corbula community to seasonality and short-term hydrological changes in the Po river

During the 20th century, increased nutrient inflow has increased the frequency and intensity of eutrophication events in the North-western Adriatic Sea. More recently, evidence of a reduction in the Po river flow and a recovery of the benthic environment were reported. We examined the role played by Po river regime and seasonality in determining the temporal pattern of macrozoobenthos variation: samples were collected from a site located 10-12km off Cesenatico during two years from October 2004 to September 2006, when the mean Po discharge remained exceptionally low. 88 taxa were found, and the community was dominated by few species: Ampelisca diadema, Lumbrineris latreillii, Corbula gibba, Aricidea claudiae, Levinsenia gracilis and Nucula nucleus account for about 80% of total abundances. The density of these species exhibited a marked seasonal variability. Moreover, the total abundance and the density of the sensitive species, A. diadema, were negatively affected by several disturbance events (hypoxic conditions, frequent storms and an anomalous winter flood) that occurred between November 2005 and March 2006. The reduction of C. gibba and the increase of A. diadema densities observed in the investigated period, and verified recently by other authors could be related to the reduction in river inputs as a consequence of climatic changes.

Trans-generational plasticity in physiological thermal tolerance is modulated by maternal pre-reproductive environment in the polychaete Ophryotrocha labronica

Maternal temperature is known to affect many aspects of offspring phenotype, but its effect on offspring physiological thermal tolerance has received less attention, despite the importance of physiological traits in defining organismal ability to cope with temperature changes. To fill this gap, we used the marine polychaete Ophryotrocha labronica to investigate the influence of maternal temperature on offspring upper and lower thermal tolerance limits, and assess whether maternal influence changed according to the stage of offspring pre-zygotic development at which a thermal cue was provided. Measurements were taken on adult offspring acclimated to 18 or 30°C, produced by mothers previously reared at 24°C and then exposed to 18 or 30°C at an early and late stage of oogenesis. When the shift from 24°C was provided early during oogenesis, mothers produced offspring with greater cold and heat tolerance whenever mother–offspring temperatures did not match, with respect to when they matched, suggesting the presence of an anticipatory maternal effect triggered by the thermal variation. Conversely, when the cue was provided later during oogenesis, more tolerant offspring were observed when temperatures persisted across generations. In this case, maternal exposure to 18 or 30°C may have benefited offspring performance, while limitations in the transmission of the thermal cue may account for the lack of correlation between maternal experiences and offspring performance when mother–offspring environments did not match. Our results provided evidence for a trans-generational effect of temperature on physiological performance characterised by a high context dependency, and are discussed in the light of maternal pre-reproductive experiences.

Effects of temperature on two Mediterranean population of Dinophilus gyrociliatus (Polychaeta: Dinophilidae): II. Effects on demographic parameters

Abstract The effects of temperature on demographic characteristics of two populations from Ravenna and Genoa of the polychaete Dinophilus gyrociliatus were investigated. Temperature affects age-specific survival and fecundity and all the demographic parameters often to a different degree in the two populations. Individuals from Ravenna survive longer than those from Genoa. The most evident differences in the age-specific fecundity curves of the experimental groups are related to age at maturity and the duration of the reproductive period that are in inverse proportion to temperature. In both populations of D. gyrociliatus , the maximum daily fecundity is observed at intermediate temperatures. In all cases, the Genoa females mature earlier, attain their maximum fecundity more quickly and have a shorter reproductive period than their Ravenna counterparts. Age at maturity, fecundity during the first reproductive events and juvenile survival are by far the most important characteristics in determining the fitness of the two populations at the tested temperatures. Even though the greatest net growth rates and highest expectation of life were recorded at 12 °C in the Ravenna population, the delay in the attainment of sexual maturity means that, at this temperature, the population growth rate is lowest. The higher juvenile survivorship and the greater fecundity observed at 24 °C is counter-balanced by the early attainment of sexual maturity induced at 30 °C. The comparison of the population growth rate calculated in laboratory with field data suggests that temperature is one of the main environmental parameters determining the fitness of D. gyrociliatus .

Relationship of non-specific commensalism in the colonization of the deep layers of sediment

The macrofauna of samples collected with a box-corer from northern Adriatic Sea muddy bottoms in five survey campaigns from 1985 to 1993 has been analysed separately in sediment strata of varying depth. Samples were collected before, during and after the dumping of large amounts of inert particulate material that covered the seabed and caused an almost total defaunation. After this disturbance the seabed was recolonized by a new community This new community differed from the original one mainly on account of the abundance of Mysella bidentata, a small bivalve filter or surface deposit-feeder. In the original community Al. bidentata was confined to the more superficial sediment layers (0-5 cm) at low population density. In the new community it was very abundant and evenly distributed even in the deep layers (5-20 cm). Analysis of species association performed on data from each of the 54 corer samples collected in the last sampling period, points to a marked association between M. bidentata and Nephtys incisa in deeper sediment layers. Deep layer colonization by Mysella in association with the burrowing polychaete N. incisa suggests a case of commensalism between these two species.

Laboratory observations on predator–prey interactions between the bearded fireworm (Hermodice carunculata) and Mediterranean benthic invertebrates

ABSTRACT The bearded fireworm (Hermodice carunculata) is an amphinomid polychaete with a circumtropical Atlantic-Mediterranean distribution. In the Mediterranean Sea, very little information is available on its feeding habits and ecological functions. Here, its increasing abundance and the ability to actively prey on a keystone sea urchin species suggest potential repercussions for the structure and functioning of benthic communities. We performed laboratory feeding experiments to investigate interactions between Mediterranean H. carunculata and 12 species of sessile or sedentary invertebrates. H. carunculata preyed efficiently on 9 of the species offered. In particular, active predation of a polychaete upon nudibranchs, colonial ascidians and chitons was reported for the first time. Fireworms’ predatory ability may be due to a combination of several ‘weapons’ (large size, motility, stinging chaetae and eversible, sucking pharynx) which seems to be unique among marine worms, and could enable H. carunculata to persist also after radical changes in prey community composition and withstand selective pressures associated with ongoing environmental changes.